Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address rollover (wheels lifting) of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
During a potential vehicular rollover event, one side of the wheels starts lifting, and the roll center of the vehicle shifts to the contact patch of the remaining tires. This shifted roll center increases the roll inertia of moment of the vehicle, hence reduces the roll acceleration of the vehicle. However, the roll attitude could still increase rapidly. The corresponding roll motion when the vehicle starts side lifting deviates from the roll motion during normal driving condition.
When the wheels start to lift from the pavement, it is desirable to confirm this condition. This allows the system to make an accurate determination as to the correction.
Some systems use position sensors to measure the relative distance between the vehicle body and the vehicle suspension. One drawback to such systems is that the distance from the body to the road must be inferred. This also increases the number of sensors on the vehicle. Other techniques use sensor signals to indirectly detect wheel lifting qualitatively.
One example of such a wheel lifting determination can be found in Ford patent U.S. Pat. No. 6,356,188. The system applies a change in torque to the wheels using the available sensed signals and the available calculated signals to determine wheel lift. The output from such a wheel lifting determination unit can be used qualitatively to detect, monitor and predict potential rollover event. If the qualitative determination indicates a positive flag for potential rollovers, a quantitative determination of how severe the rollover might be through estimated vehicular roll angle is conducted. This method is an active determination since the basis of the system relies on changing the torque of the wheels by the application of brakes or the like. In some situations it may be desirable to determine wheel lift without changing the torque of a wheel.
It would therefore be desirable to provide a rollover detection system that improves reliability in predicting the occurrence of wheel lift during the operation of the automotive vehicle.